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Recently, the combination of beamforming (BF) and space-time block coding (STBC) has been widely studied in wireless communications, and is recognized as an efficient means to improve the system performance. In this paper, an open-loop adaptive space-time transmit scheme for correlated fading channels is presented. A hybrid system combining adaptive BF with STBC is first developed based on the model of the equivalent scaled additive white Gaussian noise (AWGN) channel induced by STBC, in which the maximization of the output mean signal-to-noise ratio (SNR) and the minimization of the symbol error rate (SER) upper bound are used as the design criteria. Then, a method to efficiently calculate the downlink beamforming weight vectors from the uplink channel correlation matrix is presented, so that the feedback of channel statistics from the receiver to the transmitter can be avoided. The main benefit of the proposed scheme is that it can achieve a nearly optimal performance with low implementation complexity. Next, utilizing the Laplace transform, the SER performance of the system with the new transmit scheme is analyzed by considering the three most widely used modulations, namely, -PAM, -PSK and square -QAM. Finally, analytical and simulation results are given to demonstrate the validity and superiority of the proposed method.
Selected Topics in Signal Processing, IEEE Journal of (Volume:2 , Issue: 2 )
Date of Publication: April 2008